The invention relates to a metallic material comprising at least one refractory material or an alloy based on at least one refractory material. The invention also relates to the manufacture and use of the metallic material.
Particularly in the area of medical technology, wires, pipes, or bands made of noble metals (e.g., platinum or platinum alloys) or of refractory metals Y of the group (chromium, cobalt, molybdenum, nickel, niobium, rhenium, tantalum, titanium, wolfram, zirconium) and their alloys (for example, NbZr1 (1 wt % Zr) or TaNbxYz (where x and z represent possible atomic ratios of Nb and Y)), as well as stainless steels or nitinol, are used for a variety of purposes. Most metallic materials which find use for various medical applications represent a compromise between good compatibility, handlability, good mechanical properties, workability, and the associated costs.
The requirements for materials, such as used for stents, are many. Materials are needed with the highest rigidity possible. High rigidity allows the required strut cross-sections to be reduced to an appropriate minimum. The criterion here is to achieve the highest possible supporting effect with the lowest possible amount of material introduced into the human body. Reduction of the amount of metal also results in improvement of the core spin compatibility of the stent, since less material results in fewer artifacts during examination with core spin tomography.
At the same time, with the reduction in the amount of material, however, the visibility of the parts (for example, stents) is decreased in an X-ray image. This disadvantage can be avoided by providing a layer of highly X-ray-visible material (generally a noble metal with a high atomic number) on the structure, or equipping it with so-called markers. In both cases, there is a certain risk that this application may create corrosive potentials between the different materials, which can lead to the weakening or dissolution of the parts affected.
Some known materials for stents (stainless steel, CoCr alloys, MP35N or nitinol) are generally not helpful, or contain additional chemical components that are not considered biocompatible.
Refractory metals exhibit relatively good X-ray contrast. In addition, there are many combinations in which they are soluble in each other, allowing the possibility of varying the X-ray contrast and adjusting it specifically.
Metallic materials of the type characterized above are known, for example, from U.S. Pat. No. 6,358,625 B1. Here, anode wires of niobium or tantalum are disclosed, which are treated with oxygen to improve the bond, in such a way that an enrichment results on the surface in the range of 35 atomic % in a layer of about 50 nm thick. This enrichment produces a surface layer with niobium oxide or tantalum oxide, which is used as a sintering aid in the manufacture of capacitors.
Espe, Materials Science of High-Vacuum Technology, vol. 1, pages 146 through 149, VEB German publisher of the German sciences, Berlin (1959) describes a surface oxidation of niobium, wherein a brittleness of the material is introduced with increasing oxygen uptake, whereby the ductility of the material therefore decreases. In particular, the reduction in elongation at break can be seen in Table T3.7-2b. Thus, this teaching also recommends the reduction of oxygen.
From U.S. Pat. No. 5,242,481, in agreement with the disclosure of Espe, powder-metallurgically manufactured products of tantalum or niobium are known, which have an oxygen content of less than 300 μg/g. Likewise in agreement therewith, it is known from German published patent application DE 37 00 659 A1 that tantalum becomes brittle if it is exposed to oxygen-containing atmospheres at higher temperatures. It thereby loses its ductility.